Spinal implant, driver tool and nut guide

ABSTRACT

A spinal implant for an osteosynthesis device, which implant includes an implant body  18  having a rod retaining section  28, 54  to retain a connecting rod  14,  and an anchoring screw section  20  extending from the implant body. The anchoring screw section  20  has a spinal opening  24, 46  to permit borne ingrowth therein. The rod retaining section  28, 54  includes a rod movement stabilizing means  35.  A nut member  32, 52  is screwed onto a head section of the implant body, and has a tool engagement groove  56.  A driver tool  70, 78  has an engaging segment or tip  72   a,    78   c,  that engages with the tool engagement groove of the nut member. A nut guide  80  is provided for momentarily guiding and retaining the nut in place such that it is subsequently removed to the head section of the implant body with the use of the driver tool  78  passing through the nut guide.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to spinal implants forosteosynthesis devices and, more particularly, to a spinal implant, adriver tool specifically suited for the spinal implant, and a nut guidesuited for the spinal implant.

[0002] In recent years, various research and development have beenattempted to provide a spinal implant that is designed to achieveadaptation to differences in alignment, augulation and depth ofpenetration of adjacent spinal implants anchored to vertebral bodieswhich are spaced from one another.

[0003] One of such implants is disclosed in U.S. Pat. No. 5,154,719.This device includes a head portion having a pair of upright brancheswhich are internally threaded and which has a U-shaped recess, and ascrew portion projecting from the head portion. A connecting rod isreceived in the two branches, which are fixed in place by means of aring member. During this operating step, there exist some difficultiesin precisely adjusting the orientation of the U-shaped recesses of thespaced spinal implants anchored in vertebral bodies, angulation of thespinal implants and depth of the spinal implants, with a resultantundesirable fixation of the implants and the connecting rod. Since,further, the screw portion is composed of a solid material and the screwportion is merely anchored in the vertebral body. Accordingly, after thespinal implant penetrates in the vertebral body, fixation of the spinalimplant is unstable and is liable to be undesirably affected withexternal forces when they are applied to the spinal implants.

[0004] U.S. Pat. No. 5,879,351 discloses a spinal osteosynthesis devicecomprising at least one vertebral rod, pedicle screws and deformableconnectors. In this prior art, each of the pedicle screws is composed ofthe same solid material as in the prior art discussed above, and adifficulty is similarly encountered in reliably fixing the pedicle screwin the vertebral body. Further, each of the deformable connectors has anoblong opening through which a head portion of the screw extends andeach connector is resiliently supported between a cylindrical base and anut, with a given space being provided for permitting relative movementof the vertebral rod. With such a structure, the spinal implant iscaused to have a large number of component parts, resulting in acomplicated structure and an increased cost.

[0005] In known techniques, it has been a usual practice to lock a pluginto the spinal implant by means of a tool holder. In practice, thereare two types of head section formed with two upright branches, that is,a first type of head section having an internally formed thread, and asecond type of head section having an outwardly formed thread. In thefirst type, the plug is screwed in the internal thread of the headsection. In this event, the two branches are loosened, thereby providinga difficulty in tightly locking the connecting rod in the spinalimplant. On the contrary, in the second type, the plug is screwed ontothe outer thread of the head section. In this event, an outer peripheryof the plug has a hexagonal profile, and a driver tool having ahexagonal groove is brought into engagement with the outer hexagonalwall of the plug for rotating the plug. In this event, since the drivertool has an outer diameter larger than that of the plug, increasing anoccupying space for rotating the driver tool. Under these conditions,when two spinal implants are anchored in adjacent vertebral bodies in arelationship closer to one another, the outer periphery of the drivertool is liable to interfere with the adjacent plug of the spinalimplant, causing difficulties in rotating operation of the driver tool.

SUMMARY OF THE INVENTION

[0006] Who The present invention has been made with a view to overcomingthe various disadvantages encountered in prior art devices and it istherefore an object of the present invention to provide a spinal implantfor an osteosynthesis device, a driver tool for rotating the spinalimplant, and a nut guide for guiding the implant body and the drivertool.

[0007] According to a first aspect of the present invention, there isprovided a spinal implant for an osteosynthesis device having avertebral connecting rod for interconnecting vertebral bodies spacedfrom one another. The spinal implant comprises an implant body includinga head section having a threaded portion and a rod retaining recessopening outward for retaining the connecting rod therein, and ananchoring screw section longitudinally extending from the head sectionand adapted to be screwed into the vertebral body, a retaining plugcoupled to the head section of the implant body to maintain theconnecting rod in place, and rod movement stabilizing means directlylocated in at least one of the rod retaining recess and the retainingplug for allowing pivotal movement of the connecting rod in theretaining recess, thereby preserving mobility to the connecting rod.

[0008] According to a second aspect of the present invention, there isprovided a driver tool for a spinal implant having an implant body andan anchoring screw portion, and a nut member screwed onto a head portionof the implant body and having an upper wall formed with a toolengagement groove. The driver tool comprises an elongated shaft, and atubular tool end having substantially the same diameter as that of thenut member, the tubular tool end having an engaging segment adapted toengage with the engagement groove formed on the upper wall of the nutmember.

[0009] According to a third aspect of the present invention, there isprovided a nut guide for guiding a nut member of a spinal implant havingan implant body and an anchoring screw section, and for guiding a drivertool having a lower end formed with a nut engagement tip, wherein avertebral connecting rod is retained with a pair of the spinal implantto be anchored into vertebral bodies. The nut guide comprises a gripsection, and a hollow cylindrical shaft extending from the grip sectionand adapted to permit insertion of the driver tool therein, thecylindrical shaft having a lower distal end formed with a rod engagingsegment for engaging with and retaining the connecting rod to place thelower distal end in a fixed place, and a threaded bore formed rearwardof the rod engaging segment for momentarily receiving the nut membertherein. The cylindrical shaft allows the driver tool to pass thereinsuch that the nut engagement tip is brought into engagement with the nutmember guided with the cylindrical shaft to move the nut member from thethreaded bore to the implant body of the spinal body.

[0010] Other aspect and advantages of the invention will become moreapparent from the following description, taken in conjunction with theaccompanying drawings, illustrating by way of example the principles ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a schematic view of an osteosynthesis deviceincorporating a first preferred embodiment of a spinal implant accordingto the present invention, with a connecting rod being utilized tointerconnect spaced vertebral bodies by means of plural spinal implants;

[0012]FIG. 2 is a side view illustrating the relationship between theplural spinal implants and the associated connecting rod;

[0013]FIG. 3 is an enlarged front view of the first preferred embodimentof the spinal implant according to the present invention;

[0014]FIG. 4 is a cross sectional view of the spinal implant shown inFIG. 3;

[0015]FIG. 5 is another cross sectional view of the spinal implant shownin FIG. 3;

[0016]FIG. 6 is a left side view of the spinal implant shown in FIG. 3;

[0017]FIG. 7 is an enlarged front view of a second preferred embodimentof a spinal implant according to the present invention;

[0018]FIG. 8 is an enlarged front view of a third preferred embodimentof a spinal implant according to the present invention, with theconnecting rod being shown as being fastened by the spinal implant ofthe third preferred embodiment;

[0019]FIG. 9 is en enlarged, front view of a nut member forming part ofthe spinal implant shown in FIG. 8;

[0020]FIG. 10 is an enlarged, plan view of the nut member shown in FIG.8;

[0021]FIG. 11 is an enlarged, bottom view of the nut member shown inFIG. 8;

[0022]FIG. 12 is an enlarged, front view of a driver tool specificallysuited for use in the nut member shown in FIG. 8;

[0023]FIG. 13 is an enlarged view for illustrating the relationshipbetween the spinal implant and a nut guide of a fourth preferredembodiment according to the present invention;

[0024]FIG. 14 is a side view of the osteosynthesis device shown in FIG.13;

[0025]FIG. 15 is an enlarged, exploded view of the nut guide shown inFIG. 13; and

[0026]FIG. 16 is an enlarged side view of the nut guide shown in FIG.13.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Referring to the drawings and more particularly to FIGS. 1 and 2,a spinal osteosynthesis device, generally designated at 10, is shown asapplied to separate vertebral bodies 12 for interconnecting pluralvertebral bodies 12 in place.

[0028] The spinal osteosynthesis device 10 includes an elongatedvertebral connecting rod 14 retained by a pair of spinal implants 16 ofa first preferred embodiment according to the present invention. Each ofthe spinal implants 16 penetrates each vertebral body 12 in a manner aswill be discussed below in detail. The connecting rod 14 is made ofmalleable, elastically deformable material having a large elasticcapacity, permitting elastic deformation necessary for adaptation it todifferences in alignment, angulation and depth of penetration of theimplants 16.

[0029] Referring now to FIGS. 3 and 4, the spinal implant 16 includes acylindrical implant body 18 for firmly retaining the connecting rod 14in place, and an anchoring screw section 20 that longitudinally extendsfrom the implant body 18 and adapted to be anchored in the vertebralbody 12 (see FIGS. 1 and 2).

[0030] The anchoring screw section 20 has a hollow internal fusionchamber 22, and a plurality of spinal openings 24 each of which iscomposed of a longitudinally extending elongated slit. Each of theelongated slit 24 transversely extends through the anchoring screwsection 20 from one side to the other side and communicates with theinternal fusion chamber 22 to permit borne ingrowth into the fusionchamber 22. Thus, the anchoring screw section 20 has a plurality ofcircumferentially spaced, elongated wall segments 26 defined between thehollow internal fusion chamber 22 and the plural slits 24, providingelastic deformation to the anchoring screw section 20 to allowadaptation of any positioning of the threaded section while permittingan effective fixation without impairing the borne anchorage.

[0031] A head portion of the implant body 18 is formed with a U-shapedrod retaining recess 28 that opens outward, and an internally threadedbore 30 extending in a longitudinal direction at a position adjacent therod retaining recess 28. A disc shaped nut member 32 is screwed into theinternally threaded bore 30, thereby retaining the connecting rod 14 inplace in the rod retaining recess 28.

[0032] As seen in FIGS. 5 and 6, a bottom wall 34 of the retainingrecess 28 includes a rod movement stabilizing means 35 composed ofslanted engagement surfaces 36 directly located in the rod retainingrecess 28 for allowing pivotal movement of the connecting rod 14 in theretaining recess 28, thereby preserving mobility to the connecting rod14. To this end, each of the slanted engagement surface 36 is slightlyinclined from points slightly displaced from the center of axis of theimplant body 18 at an angle ⊖ from an axis of the connecting rod 14perpendicular to the axis of the implant body 18.

[0033] With such a structure, the connecting rod 14 is allowed forpivotal movement within a range defined by the slanted engagementsurfaces 36 of the retaining recess 28 of the implant body 18. Thus, theslanted engagement surfaces 36 of the rod movement stabilizing means 35is defined in the retaining recess 28 of the implant body 18, allowingthe connecting rod 14 to be inclined.

[0034] Although, the connecting rod 14 is inclined in a plane involvingthe center of axis of the implant body 18, the slanted engagementsurface 36 of the rod movement stabilizing means 35 may be modified suchthat the connecting rod 14 is allowed to be slightly inclined in a planecrossing the central axis of the implant body 18. More particularly, asshown by a phantom line in FIG. 6, the retaining recess 28 has inclinedengagement surfaces 40 formed in a longitudinal direction in right andleft directions in FIG. 6, except for the threaded portion 38.

[0035] With the structure discussed above, the plural spinal implants 16are screwed into and anchored in separate vertebral bodies 12 in amanner as shown in FIGS. 1 and 2 such that the associated rod retainingsections 28 of two implant bodies 18 are aligned, and both ends of theconnecting rod 14 are received in the implant bodies 18. In a subsequentstep, the nut member 32 are screwed into the threaded portions 30 of theimplant bodies 18, respectively, firmly retaining the both ends of theconnecting rod 14 to clamp the same in the required position.

[0036] Due to the separate elongated wall segments 26 formed in theanchoring screw section 20, the anchoring screw section 20 is allowed tobe penetrated into the vertebral body 12 in reduced diametrical sizeowing to the inward elastic deformation of the separate elongatedsegments 26, thereby providing ease of penetration of the implant 16.Since, also, when the penetration of the anchoring screw section 20 hasbeen completed, the separate elongated wall segments 26 expand to theiroriginal position due to their restoring forces, thereby providing animproved fixation, in an early stage, of the screw section 20 to thevertebral body 12 in a highly reliable manner. Owing to the provision ofthe plurality of spinal openings defined by the elongated slits 24 andthe hollow internal fusion chamber 22, further, the spinal implant 16permits borne ingrowth into the hollow fusion chamber 22 for therebyfurther improving fixation of the implant.

[0037] In a event the both ends of the connecting rod 14 are fitted tothe retaining recesses 28 of the implant bodies 18 after the pluralspinal implants 16 are firmly fitted to the vertebral bodies 12 in amanner discussed above, if the rotational positions of the retainingrecesses 28 of the plural spinal implants 16 are not aligned with oneanother, a desired one of the spinal implants 16 may be slightlyrotated. In addition, further, when the depths of penetration of theplural spinal implants 16 are different from one another and the pluralspinal implants 16 undergo misalignment in height, the connecting rod 14is partly allowed to be suitably deformed along the slanted surface 36,absorbing a slight difference in height of the bottom walls of theplural spinal implants 16 penetrated in the vertebral bodies 12.

[0038] In other words, even when there exists a slight difference inheight between the bottom walls 34 of the adjacent spinal implants 16,the connecting rod 14 is reliably adaptable to that difference,providing improved engagement of the connecting rod in the plural spinalimplants in an easy and simplified manner.

[0039]FIG. 7 shows a second preferred embodiment of a spinal implantaccording to the present invention, with like parts bearing the samereference numerals as those used in FIGS. 1 to 5.

[0040] The spinal implant 16 of FIG. 7 differs in structure from thefirst preferred embodiment of the spinal implant in that the implantbody 18 has a rod retaining recess 40 composed of a longitudinallyextending oblong opening and a distal end of the implant body 18 has alaterally extending tool engagement groove 42. The spinal implant 16 ofthe second preferred embodiment has the same advantages as those of thefirst preferred embodiment discussed above. Other features of the secondpreferred embodiment of the spinal implant 16 are identical to those ofthe first preferred embodiment and, accordingly, a detailed descriptionof the second preferred embodiment of the spinal implant 16 is hereinomitted for the sake of simplicity.

[0041] FIGS. 8 to 11 show a third preferred embodiment of a spinalimplant according to the present invention. In FIG. 8, the spinalimplant 16 includes an implant body 18 and an anchoring screw section 20having a plurality of small apertures 46 extending in a planeperpendicular to the axis of the screw portion 20 to allow borneingrowth therein. The implant body 18 has an upper end formed with anouter thread 50, to which a nut member 52 having an upper wall formedwith tool engagement grooves 56 is screwed. The implant body 18 also hasa U-shaped retaining recess 54, with which a spherical engaging segment14 a of a connecting rod 14 engages for pivotal movement.

[0042] As best seen in FIG. 10, the implant body 18 has a pair ofupright retaining segments 18A, 18B providing relatively large spaces 62and each having an arch-shaped cross section. Thus, the uprightretaining segments 18A, 18B provide an open distal end such that whenthe spherical engaging segment 14A is retained in the U-shaped recess54, the connecting rod 14 is allowed for pivotal movement relative tothe central axis of the spinal implant 16.

[0043] The nut member 52 has a ring-shape having an inner threadengaging the outer thread 50 of the implant body 18. An upper side ofthe nut member 52 has a plurality of tool engagement grooves 56 thatcross each other in lateral direction. As best seen in FIGS. 9 and 10,the ring-shape nut member 52 receives therein a central pivot shaft 58coaxially extending through the nut member 52. A lower ends of thecentral pivot shaft 58 is integrally formed with a rod retaining member60, that includes a central, globular retaining groove 60 a, and a pairof laterally extending arch-shaped retaining grooves 60 b. As seen inFIG. 9, the rod retaining member 60 projects downward from a lowerdistal end of the nut member 52. The rod retaining member 60 has aradial length substantially equal to the diameter of the nut member 52and has a lateral width slightly smaller than the width of the rodretaining groove 54. An upper end of the central pivot shaft 58 has acircular flange 58 a having substantially the same shape as the rodretaining member 60.

[0044] In FIGS. 8 and 12, there is shown a fourth preferred embodimentof a driver tool 70 for rotating the nut member 52. The driver tool 70includes a hollow, tubular tool end 72 and an elongated shaft 74extending upward from the tubular body 72. A lower end of the tubularbody has a plurality of substantially axially extending engagingsegments 72 a that are adapted to engage with the tool engagementgrooves 56 formed on the upper wall of the nut member 52. The tubularbody 72 is designed to have a diameter substantially equal to the nutmember 52.

[0045] With such a structure discussed above, the anchoring screwsections 20 of the plural spinal implants 16 penetrates the vertebralbodies and, subsequently, the connecting rod 14 and the sphericalengaging segment 14 a are located in the rod retaining groove 54 of theimplant body 18. In next step, the rod retaining member 60 is broughtinto engagement with the rod retaining groove 54 of the implant body 18,and the nut member 52 is screwed into the outer thread 50 of the implantbody 18. The nut member 52 is rotated with the driver tool 70 of whichengaging teeth 72 a meshes with the tool engagement grooves 56 of thenut member 52, such that the nut member 52 is fixed in place. Thismovement is enhanced with the aid of the driver tool 70, providing easeof fixing operation of the nut member 52 to the implant body 18. Aspreviously discussed, since the tubular body 72 has substantially thesame diameter as the nut member 52 and an outer periphery of the tubularbody 72 of the driver tool 70 does not interfere with an outer peripheryof the adjacent retaining plug, thereby enhancing easy fixing operationsof the driver tool 70 with respect to the adjacent retaining plugslocated in a narrow space. The tool engagement grooves 56 may not belimited to the specific groove shown in FIGS. 8 and 9, but may have anyother configuration such as a bore.

[0046] FIGS. 13 to 16 show a fifth preferred embodiment of a driver toolaccording to the present invention, with the spinal implant 16 beingidentical in structure with that of the first preferred embodimentexcept that the retaining plug 32 has a non-circular, hexagonalengagement groove 32A. In the fifth preferred embodiment, an upper endof a driver tool 78 has a grip section 78 a, and a lower portion formedwith a tool end 78 b that has a hexagonal, nut engagement tip 78 c. Thedriver tool 78 is used in combination with a nut guide 80 that includesa grip section 84 and a hollow, cylindrical shaft 82. The grip section84 has an inner guide bore 84 a that is adapted to receive the gripsection 78 a of the driver tool 78. The cylindrical shaft 82 has anaxially extending through-bore 86 to guide the driver tool 78. A lowerend of the cylindrical shaft 82 has an inner threaded bore 88, a nutguide chamber 90, an engaging guide chamber 92, and a rod engagingrecess 94 that is adapted to receive the connecting rod 14. Pluralpreliminary mounting stems 98 are fixedly connected to a mounting base96 for temporarily supporting respective nut members 32 on top ends ofthe stems. The nut members 32 have the hexagonal engagement grooves 32a, respectively.

[0047] In operation, the plural spinal implants 16 are sequentiallyfixed into the vertebral bodies 12, and the connecting rod 14 issuitably located in the rod retaining recesses 28 of the implant 16. Ina subsequent step, the nut guide 80 is placed on one of the nut members32, which has been placed on the mounting stem 98, such that the nutmember 32 is guided through the nut guide hole 90 of the nut guide 80.The nut member 32 is thud held with the nut guide 80, and the nut guide80 is moved to an operating position shown in FIG. 13. In this event,the rod engaging recess 94 of the nut guide 80 is aligned with theconnecting rod 14 such that the upper portion of the implant body 18engages with the engaging guide bore 92 of the nut guide 80 in a manneras shown in FIG. 13. Then, the driver tool 78 is inserted through thenut guide 80 until the engagement tip 78 c engages with the toolengagement groove 32 a of the nut member 32, and the driver tool 78 isrotated to cause the nut member 32 to be screwed into the implant body18 of the spinal implant 16 until the nut member 32 is brought intocontact with the connecting rod 14. Accordingly, the nut member 32 iseasily secured to the implant body 18 in a highly reliable mannerwithout causing any misalignments or difficulties.

[0048] The spinal implant, the driver tool and the nut guide of thepresent invention provide numerous advantages over the prior artpractices and which include:

[0049] (A) The spinal implant includes an implant body for retaining avertebral connecting rod, and an anchoring screw section longitudinallyextending from the implant body and adapted to be anchored in avertebral body. The anchoring screw section has a plurality of spinalopenings to permit borne ingrowth therein, with a resultant improvedfixation of the spinal implant. Each of the spinal openings includes alongitudinally extending slit or laterally extending bore thatthoroughly extends from one side to the other side.

[0050] (B) The anchoring thread section may also have a hollow, internalfusion chamber communicating with the spinal openings and longitudinallyextending through the thread section to allow borne ingrowth therein.With this structure, the spinal implant can be anchored in the vertebralbody with a suitable fixing condition in an early stage and, in asubsequent stage, the spinal implant can further be firmly anchored inthe vertebral body owing to the borne ingrowth progressed in the spinalopenings and the internal fusion chamber. This results in a reliablefixation of the spinal implant relative to the vertebral body for anextended time period.

[0051] (C) A head portion of the implant body has a rod memberstabilizing means to retain the connecting rod relative to the adjacentspinal implants for adapting it to the differences in alignment betweena rod retaining section and the connecting rod, the height of the rodretaining section, and angulation and depth of penetration of theanchoring screw sections. Thus, the connecting rod can be easilysupported in place with the adjacent spinal implants without causing anycomplicated, troublesome alignments or adjustments of angulation anddepth of penetration of the anchoring screw sections.

[0052] (D) The spinal implant also includes a nut member which isdesigned to be screwed into a head portion of the implant body, with thenut member including a rod retaining member for retaining the connectingrod in place in the implant body while permitting pivotal movement ofthe connecting rod, thereby preserving smooth mobility to compensate forpositional misalignments or erroneous orientation between the adjacentspinal implants.

[0053] (E) A driver tool is employed to rotate the nut member relativeto the implant body, with the driver tool having at least one engagingsegment that engages with an engagement groove of the nut member andhaving substantially the same diameter as that of the nut member,enabling the driver tool to drive the nut member of one of the spinalimplants in an easy manner without conflicting the adjacent nut memberof the other spinal implant closely positioned to the former spinalimplant.

[0054] (F) A nut guide is proposed for reliably guiding the nut memberto be easily removed to the anchored spinal implant in a highly reliablemanner, and a driver tool is also guided by the nut guide to cause anengaging tip of the driver tool to precisely engage with the engaginggroove of the nut member of the spinal implant. Consequently, the nutmember can be smoothly coupled to the implant body within a short timeperiod without causing rotation of the implant body relative to thevertebral body.

[0055] The foregoing description of the preferred embodiments of theinvention has been presented to illustrate the principles of theinvention and not to limit the invention to the particular embodimentsillustrated. For example, although the preferred embodiments have beenillustrated and described that the anchoring screw section of the spinalimplant includes a spinal opening composed of an elongated slip orplural laterally extending bores, the spinal opening may have any othersuitable configurations such as an oblong opening or an elliptical bore.It is intended that the scope of the invention be defined by all of theembodiments encompassed within the following claims, and equivalentsthereof.

What is claimed is:
 1. A spinal implant for an osteosynthesis devicehaving a vertebral connecting rod for interconnecting adjacent vertebralbodies, comprising: an implant body including a head section having athreaded portion and a rod retaining recess opening outward forretaining the connecting rod therein, and an anchoring screw sectionlongitudinally extending from the head section and adapted to be screwedinto the vertebral body; a nut member screwed to the threaded portion ofthe head section to maintain the connecting rod in place; and rodmovement stabilizing means directly located in at least one of the rodretaining recess and the nut member for allowing pivotal movement of theconnecting rod in the retaining recess, thereby preserving mobility tothe connecting rod.
 2. A spinal implant according to claim 1 , whereinthe anchoring screw section has a plurality of spinal openings to permitborne ingrowth therein.
 3. A spinal implant according to claim 2 ,wherein the anchoring screw section also has a hollow internal fusionchamber formed in an axial direction of the thread section andcommunicating with the spinal openings to permit borne ingrowth into thespinal chamber.
 4. A spinal implant according to claim 2 , wherein thespinal opening is formed in an elongated slit axially extending along anaxis of the thread section.
 5. A spinal implant according to claim 2 ,wherein the rod retaining recess has a U-shaped profile having asemicircular bottom wall, and wherein the rod movement stabilizing meansincludes a slanted engagement surface formed on the bottom wall of therod retaining recess to permit pivotal movement of the connecting rodtherein.
 6. A spinal implant according to claim 4 , wherein theanchoring screw section has a plurality of longitudinally extending thinwall portion to permit plastic deformation of the anchoring screwsection.
 7. A spinal implant according to claim 2 , wherein the spinalopenings are formed along the axis of the anchoring screw section intransverse direction thereof.
 8. A spinal implant according to claim 1 ,wherein the head section has a threaded portion in close proximity tothe retaining recess wherein the nut member is screwed onto the threadedportion of the head section, the nut member has an upper wall formedwith a tool engagement groove adapted to engage with a driver tool.
 9. Aspinal implant according to claim 8 , wherein the tool engagement grooveincludes a transverse groove laterally formed on the distal end of thenut member.
 10. A spinal implant according to claim 9 , wherein theconnecting rod has a spherical engaging member adapted to be received inthe retaining recess of the head section, with the spherical engagingmember being retained in place with the nut member.
 11. A spinal implantaccording to claim 10 , wherein the head section includes a pair ofarch-shaped upright segments adapted to engage with first parts of thespherical member, and the nut member includes a ring-shaped structurehaving a pair of arch-shaped engagement groove adapted to engage withsecond parts of the spherical member such that the head section of theimplant body and the nut member permit pivotal movement of the sphericalmember, thereby preserving mobility to the connecting rod.
 12. A drivertool for a spinal implant having an implant body and an anchoring screwportion, and a nut member screwed onto a head portion of the implantbody and having an upper wall formed with a tool engagement groove, thedriver tool comprising: an elongated shaft; and a tubular tool endhaving substantially the same diameter as that of the nut member, thetubular tool end having an engaging segment engageable with theengagement groove formed on the upper wall of the nut member.
 13. A nutguide for guiding a nut member of a spinal implant having an implantbody and an anchoring screw section, and for guiding a driver toolhaving a lower end formed with a nut engagement tip, wherein a vertebralconnecting rod is retained with a pair of the spinal implant to beanchored into vertebral bodies, the nut guide comprising: a gripsection; and a hollow cylindrical shaft extending from the grip sectionand adapted to permit insertion of the driver tool therein, thecylindrical shaft having a lower distal end formed with a rod engagingsegment for engaging with and retaining the connecting rod to place thelower distal end in a fixed place, and a threaded bore formed rearwardof the rod engaging segment for momentarily receiving the nut membertherein; wherein the cylindrical shaft allows the driver tool to passtherein such that the nut engagement tip is brought into engagement withthe nut member guided with the cylindrical shaft to move the nut memberfrom the threaded bore to the implant body of the spinal body.
 14. A nutguide according to claim 13 , wherein the cylindrical shaft further hasa nut guide hole formed between the threaded bore and the rod engagingsegment.